Since cement clinker is obtained by mixing limestone with clay and sintering the mixture, each of sintering of the limestone and burning of heavy fuel oil causes release of carbon dioxide gas in obtaining the cement clinker. Therefore, it is said that one ton of carbon dioxide gas is generated in sintering a ton of cement clinker. In recent years, a new alternative technology to replace cement is sought because the global warming has become a worldwide concern and emission constraint of the carbon dioxide gas has become a significant subject.
Under the circumstances, a solidified ceramic body solidified at a normal temperature is getting much attention as energy-saving material which is free from limestone and sintering. This solidified ceramic body is fabricated by binding ceramic powder by means of water glass which serves as binder. In fabricating this solidified ceramic body, the water glass is mixed with filler such as metakaolin, and metal ions in the filler dissolves and reacts with the water glass. Thus, sodium silicate constituting the water glass gets cross-linked to become an inorganic polymer. Then, a dehydration-condensation reaction proceeds along with water evaporation which results in the solidified ceramic body.
Thus, it is possible to easily obtain building material such as blocks at a normal temperature without using limestone if the solidified ceramic body is fabricated by using, as is described above, the water glass to solidify the filler (although it is preferable to sinter the solidified ceramic body at 750 degrees C., this temperature is still far lower than a temperature at which the cement clinker is sintered.) Therefore, the amount of the carbon dioxide gas generated in fabricating this solidified ceramic body is far smaller than that in fabricating the cement.
However, in the above-described solidified ceramic body fabricated by using the water glass as the binder, the solubility of ceramics in the solidified ceramic body significantly changes depending on the proportion of silicon to sodium in the water glass and the degree of polymerization. Therefore, it is hard to control the solidification so as to reproductively make the solidified ceramic body have high strength. In addition, since the water glass is used in large amounts in fabricating the solidified ceramic body, evaporation of water in the water glass tends to cause the solidified ceramic body to deform and crack. This results in a problem that the mechanical strength of the solidified ceramic body is insufficient. Moreover, the evaporation of the water causes a condensation reaction which results in a problem that the dimension accuracy of the solidified ceramic body is insufficient. Moreover, since the water glass is used in large amounts in fabricating the solidified ceramic body, fractions of the water glass become prominent on the surface of the solidified ceramic body, make the solidified ceramic body stained in white, and harm the appearance of the solidified ceramic body. Moreover, since the highly viscous water glass and the ceramic powder have to be mixed well, it takes a large amount of energy and time to mix the water glass and the ceramic powder. Furthermore, in order to cause a chemical reaction between a large amount of the water glass and the ceramics, the ceramics have to have a phase composed of silicic acid or silicate not only at the surfaces thereof but also at inner portions with a certain depth from the surfaces.
As an art for solving these problems of the solidified ceramic body, which is solidified at a normal temperature and is fabricated by binding the ceramic powder by means of the water glass as the binder, non-sintering ceramics have been developed which are fabricated by activating ceramic powder through mechanochemical treatment and solidifying the activated ceramic powder through alkali treatment (see The Ceramic Society of Japan, Proceedings of 20th Autumn Symposium, p. 17.)
This art makes it easy to control the solidification, improves the mechanical strength, the dimension accuracy and the appearance of the solidified ceramic body, decreases energy consumed in fabricating the solidified ceramic body, and widens variety of resources as the raw material for the solidified ceramic body.